Semiconductor materials are widely used for the application to electronic devices such as transistors and solar cells. To evaluate carrier conduction in this semiconductor and electric characteristics of the surface state is important in manufacturing semiconductor devices having target characteristics with excellent yield.
It has been customary that an insulating film, for example, a surface protecting insulating film, a gate insulating film, a field insulating film and the like are formed on the surface of semiconductor. Interface state density between semiconductor and this insulating film considerably affects electric characteristics of semiconductor, accordingly, electric characteristics of semiconductor device and its evaluation is important.
Therefore, when characteristics of semiconductor are measured, it is not desirable that electrodes for measuring electric characteristics should be formed on the semiconductor in the state in which the insulating film was removed from the surface of the semiconductor because this method is not able to accurately measure electric characteristics of the semiconductor.
As methods for evaluating electric characteristics of semiconductor, an evaluation method based on capacity-voltage characteristic measurement using a metal/insulator/semiconductor structure has been used widely. According to this evaluation method, a bias voltage is applied to the above-described metal side, a small modulation high-frequency voltage is superimposed upon the applied bias voltage and a bias voltage and capacity characteristic based on the change of a depletion layer generated within a measured semiconductor is calculated. Then, quantity of electric charges in the insulating film and interface state density between the insulating film and the semiconductor are calculated from this voltage-capacity characteristic.
However, this measuring method encounters with a problem in accurately measuring semiconductor characteristics from the changes of this voltage-capacity characteristics because it has been customary that a semiconductor should have a thickness of greater than 10 μm in order to form depletion layers and that the change of the depletion layer is small in thin film semiconductors.
Also, other measuring method has been described in Japanese Published Patent Application No. 4-282846 in which attenuation of excess minority carriers induced within the semiconductor when pulse light is irradiated to the semiconductor, that is, life time is evaluated from the change of reflectance of light in the microwave band, thereby to examine a carrier conduction mechanism within the semiconductor.
However, in this case, in actual practice, it was difficult to directly evaluate the change of carrier concentration from the change of reflectance of light in the microwave band. Further, since a microwave generating power supply, a waveguide for guiding microwaves and the like are required, a problem arises, in which a measuring apparatus becomes complex in arrangement.